With a majority of the more than 100,000 million dental restorative treatments performed in the US each year involving the placement of resin-bonded composite materials, and the acknowledgement that a large portion of a dentist's time is consumed with revising and replacing these restorations, there is a clear need for materials with improved clinical performance. Composite restoratives not only hold an esthetic advantage over dental amalgams, but they offer a means to adhesively bond the restoration to dentin and enamel. However, due to polymerization shrinkage stresses that challenge this critical interface from the time of placement, a strong, intact margin can not currently be reliably obtained. A highly versatile technique has been developed recently for preparing nano-scale (5 - 100 nm) polymeric particles with control over branching, chemistry and reactive site placement. These reactive nanogels can be dispersed readily at high concentrations in secondary monomers, which then infiltrate and subsequently copolymerize with the prepolymer additives. This approach has provided substantial reductions in polymerization shrinkage and stress, as well as a demonstrated ability to improve the strength of a model dental resin and composite. The proposed project would extend the positive preliminary results into practical examples of highly filled, low stress, nanogel-modified composites for restorative applications while also developing new sealant materials that rely on interpenetrating polymer networks to achieve dramatically reduced levels of free monomer during placement. Bioactive sealants based on nanogels that display anti-bacterial and potentially MMP-inhibiting properties will also be developed and demonstrated. The application is constructed around three aims: i) fundamental studies of nanogel synthesis designed to produce well controlled nanogel structures with predictable properties with a primary focus on a balance between high nanogel contents in monomeric matrices with practically useful viscosities and optical properties; ii) application of nanogels in dental composites where greater than proportional reductions in stress, relative to the nanogel content, will be sought while also improving the fracture toughness of potentially bulk filling composites that combine high loading levels of both nanogel and novel surface-treated inorganic fillers; and iii) use of nanogels to create sealant materials with interpenetrating polymer networks that form with high conversion and a reduced sensitivity to oxygen inhibition, which means more stable materials with much less leachable compound release. The sealant material platform will be further extended to demonstrate the potential bioactivity of polymers with chemically integrated nanogels that convey bactericidal and MMP- inhibition properties.